1. Field of the Invention
The present invention relates to a Fabry-Perot laser apparatus mode-locked to a multi-frequency lasing light source capable of implementing a cost-effective light source used for optical communications based on Wavelength Division Multiplexing (WDM) without a high-priced external modulator and an optical transmission apparatus using the Fabry-Perot laser apparatus mode-locked to the multi-frequency lasing light source.
2. Description of the Related Art
Conventionally, a Passive Optical Network (PON) based on WDM provides very high speed broadband communication services using a specific wavelength allocated to each subscriber. Accordingly, communication security can be ensured, and a specific communication service or an extension of communication capacity that the subscriber needs can be readily accommodated. Moreover, a specific wavelength can be allocated to a new subscriber and hence the number of subscribers can be increased. In spite of the above-described advantages, because a Central Office (CO) and each subscriber site need a light source for a specific wavelength and an additional wavelength stabilizing circuit for stabilizing a wavelength of the light source, subscriber costs are too high. For this reason, the PON based on the WDM is not commercialized. To implement the PON based on the WDM, the development of a cost-effective WDM-based light source is required.
A PON based on the WDM using a Distributed FeedBack (DFB) laser array, an Multi-Frequency Laser (MFL), a spectrum-sliced light source, an Fabry-Perot (FB) laser mode-locked to incoherent light as the WDM-based light source has been proposed. However, processes for manufacturing the DFB laser array and the MFL are complicated, and the DFB laser array and the MFL for precision wavelength selectivity and wavelength stabilization of the WDM-based light source are high-priced devices.
A spectrum-sliced light source being actively researched can provide the increased number of wavelength division channels by spectrum-slicing optical signals having wide bandwidth using an optical filter or a Waveguide Grating Router (WGR). Thus, a light source for a specific wavelength and equipment for wavelength stabilization are not needed. There are proposed an Light Emitting Diode (LED), an Super-Luminescent Diode (SLD), an FP laser, a fiber amplifier light source, a ultra short pulse light source, etc. as WDM-based light sources. The LED and the SLD proposed as the WDM-based light sources provide very wide optical bandwidth and are inexpensive. However, because the LED and the SLD provide relatively narrower modulation bandwidth and relatively lower output power, they are appropriate as light sources for upstream signals, which are modulated at a lower rate than downstream signals. The FP laser is an inexpensive and high-power device, but cannot provide the increased number of wavelength division channels because of the FP laser's narrow bandwidth. Moreover, when the spectrum-sliced signal outputted by the FP laser is modulated,there is a problem of degradation of performance due to mode partition noise. The ultra short pulse light source has a very wide spectral band and coherence, but has lower stability and pulse width of only several ps. It is thus difficult to implement the microwave pulse light.
A spectrum-sliced fiber amplifier light source has been proposed that is capable of spectrum-slicing Amplified Spontaneous Emission (ASE) light generated from an optical fiber amplifier and providing the increased number of high-power wavelength division channels, in place of the above-described light sources. However, the spectrum-sliced light source requires a high-priced external modulator such as a LiNbO3 modulator so that respective channels transmit different data.
On the other hand, the FP laser mode-locked to incoherent light is used for transmitting mode-locked signals outputted by injecting spectrum-sliced signals into the FP laser with no isolator after spectrum-slicing optical signals of wide bandwidth generated from the incoherent light source such as the LED or the fiber amplifier light source using the optical filter or the WGR. Where the spectrum-sliced signals of predetermined output power or more are injected into the FP laser, the FP laser generates and transmits only signals of a wavelength equal to a wavelength of the injected spectrum-sliced signals. The FP laser mode-locked to incoherent light directly modulates FP laser light on a data signal basis, thereby performing cost-effective data transmission. However, in order to output the mode-locked signals appropriate for long-distance transmission at high speed, the spectrum-sliced signal injected into the FP laser must behigh-power optical signals of wide bandwidth. Moreover, where the incoherent light of bandwidth wider than a mode interval of output signals of the FP laser is injected to transmit high-speed data, the output signals of the mode-locked FP laser have signals of a plurality of wavelengths distributed on the basis of the mode intervals. In this case, long-distance transmission cannot be implemented due to the effect of dispersion of an optical fiber.